linux-kernel - [tip:x86/syscall] arm64/syscalls: Check address limit on user-mode return

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Date:   Sat, 8 Jul 2017 05:10:37 -0700
From:   tip-bot for Thomas Garnier <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     viro@...iv.linux.org.uk, arnd@...db.de, luto@...nel.org,
        keescook@...omium.org, tglx@...utronix.de, pmladek@...e.com,
        linux@...linux.org.uk, dave.hansen@...el.com, luto@...capital.net,
        catalin.marinas@....com, thgarnie@...gle.com, panand@...hat.com,
        jpoimboe@...hat.com, mbenes@...e.cz, linux-kernel@...r.kernel.org,
        mark.rutland@....com, hpa@...or.com, mingo@...nel.org,
        dhowells@...hat.com, will.deacon@....com, oleg@...hat.com,
        riel@...hat.com, wad@...omium.org, cmetcalf@...lanox.com,
        pbonzini@...hat.com
Subject: [tip:x86/syscall] arm64/syscalls: Check address limit on user-mode
 return

Commit-ID:  cf7de27ab35172a9240f079477cae3146a182998
Gitweb:     http://git.kernel.org/tip/cf7de27ab35172a9240f079477cae3146a182998
Author:     Thomas Garnier <thgarnie@...gle.com>
AuthorDate: Wed, 14 Jun 2017 18:12:03 -0700
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Sat, 8 Jul 2017 14:05:33 +0200

arm64/syscalls: Check address limit on user-mode return

Ensure the address limit is a user-mode segment before returning to
user-mode. Otherwise a process can corrupt kernel-mode memory and
elevate privileges [1].

The set_fs function sets the TIF_SETFS flag to force a slow path on
return. In the slow path, the address limit is checked to be USER_DS if
needed.

[1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990

Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Mark Rutland <mark.rutland@....com>
Cc: kernel-hardening@...ts.openwall.com
Cc: Will Deacon <will.deacon@....com>
Cc: David Howells <dhowells@...hat.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Miroslav Benes <mbenes@...e.cz>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Pratyush Anand <panand@...hat.com>
Cc: Russell King <linux@...linux.org.uk>
Cc: Petr Mladek <pmladek@...e.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: Will Drewry <wad@...omium.org>
Cc: linux-api@...r.kernel.org
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Link: http://lkml.kernel.org/r/20170615011203.144108-3-thgarnie@google.com

---
 arch/arm64/include/asm/thread_info.h | 4 +++-
 arch/arm64/include/asm/uaccess.h     | 3 +++
 arch/arm64/kernel/signal.c           | 5 +++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 46c3b93..c5ba565 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -86,6 +86,7 @@ struct thread_info {
 #define TIF_NOTIFY_RESUME	2	/* callback before returning to user */
 #define TIF_FOREIGN_FPSTATE	3	/* CPU's FP state is not current's */
 #define TIF_UPROBE		4	/* uprobe breakpoint or singlestep */
+#define TIF_FSCHECK		5	/* Check FS is USER_DS on return */
 #define TIF_NOHZ		7
 #define TIF_SYSCALL_TRACE	8
 #define TIF_SYSCALL_AUDIT	9
@@ -107,11 +108,12 @@ struct thread_info {
 #define _TIF_SYSCALL_TRACEPOINT	(1 << TIF_SYSCALL_TRACEPOINT)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_UPROBE		(1 << TIF_UPROBE)
+#define _TIF_FSCHECK		(1 << TIF_FSCHECK)
 #define _TIF_32BIT		(1 << TIF_32BIT)
 
 #define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
 				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
-				 _TIF_UPROBE)
+				 _TIF_UPROBE | _TIF_FSCHECK)
 
 #define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
 				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 7b8a047..ced7a7c 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -45,6 +45,9 @@ static inline void set_fs(mm_segment_t fs)
 {
 	current_thread_info()->addr_limit = fs;
 
+	/* On user-mode return, check fs is correct */
+	set_thread_flag(TIF_FSCHECK);
+
 	/*
 	 * Enable/disable UAO so that copy_to_user() etc can access
 	 * kernel memory with the unprivileged instructions.
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index c7b6de6..0f02791 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -25,6 +25,7 @@
 #include <linux/uaccess.h>
 #include <linux/tracehook.h>
 #include <linux/ratelimit.h>
+#include <linux/syscalls.h>
 
 #include <asm/debug-monitors.h>
 #include <asm/elf.h>
@@ -408,6 +409,10 @@ asmlinkage void do_notify_resume(struct pt_regs *regs,
 	 * Update the trace code with the current status.
 	 */
 	trace_hardirqs_off();
+
+	/* Check valid user FS if needed */
+	addr_limit_user_check();
+
 	do {
 		if (thread_flags & _TIF_NEED_RESCHED) {
 			schedule();